Look Up. Look Down. And Seal the Big Air Leaks First.

Attic

Nowadays, most homeowners understand that a "leaky" home creates comfort problems and imposes limitations on energy efficiency. But what's the best way to address the problem?

Google "energy efficiency improvements," and you're sure to find many well-intentioned articles advising you to:

  • Caulk around windows and doors
  • Replace old windows or add storm windows
  • Replace old exterior doors
  • Beef up your weatherstripping
  • Caulk around outlets on exterior walls
  • Increase the R-value of your insulation

And so on. While many of these improvements probably will improve energy efficiency and comfort on a small scale, there couldn't be a more clear-cut case of missing the forest for the trees.

The biggest air leaks aren't around windows and doors.

If you're determined to tighten your home envelope by sealing the gaps where air enters and leaves, all you have to do is look up. Then look down. These are where the biggest leaks are.

We know. You can't see them. They aren't as obvious as leaks around windows, which is why most people don't realize they're there.

Here's how to find them: The next time you go inside your attic or crawl space, take note of all the electrical, plumbing, and air duct penetrations. In most homes, there are wires and pipes galore! Ceiling fans and recessed lighting are big offenders, too.

When contractors installed that equipment, they had to drill or cut holes in your ceiling or floor. More often than not, they make the holes bigger than they need to be, allowing lots of air to escape.

These are the biggest gaps in your home envelope. They're the ones you should seal first.

In most homes, sealing these leaks saves much more on utility bills and improves comfort over and beyond what you gain from replacing your windows - even if you purchase the newfangled, foam-filled models with low-e glass! It's a little messy because you either have to lift up or temporarily remove attic or crawl space insulation. But it's well worth the trouble.

And the fact that you're eliminating the biggest leaks is only part of the story.

Before sealing leaks, understand the stack effect.

Warm air rises. You knew that, right?

Did you know that it also sinks? That little fact often surprises people, but it's true in some circumstances. The important thing to remember, though, is that air inside a closed system, like your home, travels up and down. We call this phenomenon the "stack effect". The biggest pressure boundaries in your home are at the top and bottom, not the sides.

Here's how it works in winter: Cold, dense air enters from below (air leaks in your crawl space) and pushes warm air upwards, through leaks in your attic.

In the summertime, things work differently. The air outside is warmer; it enters through your attic while cooler, denser air inside your home escapes through leaks in the bottom of the envelope.

What does all of this mean in the context of air sealing? Basically, the relative size of gaps at the top and bottom of the envelope isn't the only reason to seal your attic and crawl space first. The fact that more air enters and escapes from those areas anyway means they should be your top priority when pursuing energy improvements.

When it comes to home performance, here's how to proceed

To confirm whether your attic and crawl space are the biggest sources of air leakage - and they almost always are! - you should really invest in a home assessment from a Building Performance Institute-certified professional. The assessment will also reveal other major air sealing opportunities that are unique to your home.

That being said, following these steps usually results in maximum energy savings and prioritizes the most significant comfort improvements:

  1. Seal attic and crawl space air leaks: You're addressing the biggest pressure boundaries, and you're probably eliminating the biggest leaks at the same time.
  2. Increase attic insulation and encapsulate the crawl space: After you've sealed attic air leaks, it might make sense to increase the R-value of your insulation - especially if you've got old batts labeled R-19 or below. If your air handler is in your attic, consider using spray foam insulation to bring all of your indoor HVAC equipment and ductwork into the building envelope. Crawl space encapsulation does the same for your crawl space and offers other benefits as well.
  3. Caulking and air sealing around windows and doors: Until pretty recently, most window and door installers just stuffed fiberglass around each unit and covered it up with trim. Fiberglass isn't an air barrier, though. To properly seal around windows and doors, you need to remove the trim, yank out the fiberglass, and replace it with low-expansion spray foam.
  4. Caulking and air sealing other small gaps and cracks: Only worry about electrical outlets and other random wall penetrations after you've dealt with the big stuff.

Notice how "window replacement" didn't make our list? Replacing your windows is expensive and doesn't provide much ROI in terms of energy savings and comfort - at least not when you compare it to sealing your attic and crawl space. The same goes for replacing HVAC equipment. Should you replace it when it's old and worn out? Definitely. But replacing it as a "quick win" for better efficiency and comfort isn't always the best choice.

Instead, seal leaks at the top and bottom of the envelope. You'll probably be amazed at the comfort gains.